linux-kernel - Re: Pinmux bindings proposal

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Message-ID: <20120118153256.GB22818@atomide.com>
Date:	Wed, 18 Jan 2012 07:32:56 -0800
From:	Tony Lindgren <tony@...mide.com>
To:	Shawn Guo <shawn.guo@...aro.org>
Cc:	Grant Likely <grant.likely@...retlab.ca>,
	"linus.walleij@...ricsson.com" <linus.walleij@...ricsson.com>,
	"devicetree-discuss@...ts.ozlabs.org" 
	<devicetree-discuss@...ts.ozlabs.org>,
	"s.hauer@...gutronix.de" <s.hauer@...gutronix.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"rob.herring@...xeda.com" <rob.herring@...xeda.com>,
	"kernel@...gutronix.de" <kernel@...gutronix.de>,
	"cjb@...top.org" <cjb@...top.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Dong Aisheng <dongas86@...il.com>
Subject: Re: Pinmux bindings proposal

* Shawn Guo <shawn.guo@...aro.org> [120118 05:57]:
> On 18 January 2012 22:13, Tony Lindgren <tony@...mide.com> wrote:
> > Hi,
> >
> > * Grant Likely <grant.likely@...retlab.ca> [120116 09:55]:
> >> On Fri, Jan 13, 2012 at 12:39:42PM -0800, Stephen Warren wrote:
> >> >                 pinmux =
> >> >                         <"default" &pmx_sdhci_active>
> >> >                         <"suspend" &pmx_sdhci_suspend>;
> >> >
> >> >                 /* 1:n example: */
> >> >                 pinmux =
> >> >                         <"default" &pmx_sdhci_mux_a>
> >> >                         <"default" &pmx_sdhci_pincfg_a>
> >> >                         <"suspend" &pmx_sdhci_mux_a>
> >> >                         <"suspend" &pmx_sdhci_pincfg_a_suspend>;
> >>
> >>
> >> Yeah, don't do this.  Mixing phandle, string and cell values in a
> >> property gets messy and could become troublesome to parse.  I've
> >> backed away from it in the clk binding.
> >
> > Yup, that's because the string is embedded directly into the mixed
> > mode array and will likely make the following data unaligned. That
> > means it's extremely flakey to parse, and will lead into horrible
> > errors if you have typos in the .dts file.. Tried that and gave up
> > on it.
> >
> > I think I've found a way to avoid using names at all, assuming we set
> > each pin as a phandle for the drivers to use :)
> >
> The problem with doing that is we will have to represent each pin as a
> node in device tree.  For imx6q case, we have 197 pins.  Doing so will
> bloat the device tree.

Sure there's some overhead. I've got it working with 220 pins, it's
not too bad as threre's not much string parsing involved.

I don't have all the devices mapping the pins though. The .dtb for
omap4 is about 25k now.

If we wanted to avoid adding phandles for each pin, then we could do:

serial@...8020000 {
	compatible = "ti,8250";
	reg = <0x48020000 0x100>;
	reg-shift = <2>;
	interrupts = <106>;

	/* controller, offset, value */
	pins = <&mux1 0xabcd 0x10
                &mux1 0xabcf 0x0>;
};

But then the .dts file becomes an unreadable matrix unless we have
a preprocessor..

Regards,

Tony
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